Have you ever seen the beautiful Grevillea leucopteris? We have it growing far from its home in Western Australia on the northern side of Howson Hill in the Australian Garden at Cranbourne. When in flower it has large trusses of cream-white flowers arching over the surrounding garden – just magnificent. The Herbarium in Western Australia knows this beauty by the common name White Plume Grevillea. It is however more often known by another common name ‘Old Socks’ – as to some people these otherwise beautiful flowers have a very unpleasant smell indeed.
Recently the Royal Botanic Gardens Victoria at Cranbourne Gardens, was lucky enough to host a visit from Dr Sandy-Lynn Steenhuisen from the Department of Biological Sciences, University of Cape Town, South Africa. Sandy is a pollination and scent ecologist looking at the evolution of the perfumes produced by the flowers of the ancient plant family Proteaceae.
The Proteaceae are a family of plants predominately distributed in the southern hemisphere which is a legacy of their ancient origins on the super continent Gondwana. The most famous members of the family are probably the king protea of South Africa and the waratah of Australia. The family contains 83 genera of which Banksia, Grevillea, Hakea, Dryandra and Macadamia would be the most familiar to Australians.
During her visit Sandy explained that most of the time the reason that plants are producing floral scents is to ensure effective procreation of their species. Pollinators are attracted to flowers for a variety of reasons: it might be the colour of the flower, the nectar reward produced in the flower or the scent. Similar traits that unrelated flowers have evolved to attract a shared pollinator are called pollination syndromes.
I asked Sandy why her work on pollination syndromes is important. Sandy talked about our need for more information about the mutual relationships that plants rely on within their wild communities. Plants may become rare in the wild because their specific pollinator has disappeared. It becomes impossible for us to use techniques such as restoration ecology when we don’t know who the specific pollinator is for many species. There is no point replanting a species into the wild if its pollinator no longer exists in that location. More complicated than just the birds and the bees, plants rely on many different animals for pollen transfer including bugs and beetles, and as unlikely as it might seem, mammals.
So far ecologists have discovered that unrelated plants that share similar pollinators often have similar floral traits such as colour or flower shape. It is thought that the different preferences of pollinators have, through natural selection, led to the almost infinite diversity in floral forms we now enjoy.
Technological advances in the detection and analysis of scent means that ecologists have been able to study which pollinators have preferences for which scent compounds. This work has enabled ecologists to understand that in bird-pollinated systems the flowers are usually unscented. Insects tend to favour fragrant fruity scents and small mammals are attracted to cheesy, yeasty and fermented food (or possibly old sock) odours.
Sandy explained that:
“Closely related plant species using different types of pollinators may be emitting different scents for attraction. By mapping scent profiles and pollination systems onto family trees, we can assess trends in the evolution of scent and associations with different pollinators. By understanding the role of floral scent in attracting pollinators, we can better understand plant-pollinator interactions and how to conserve these relationships”.
Unexpected findings from Sandy’s work have included the role of carnivorous mammals such as mongoose and genets in pollination in South Africa.
In collaboration with Dr Trevor Edwards, from La Trobe University, Sandy aims to survey the scents of as many South African and Australian Proteaceae as possible knitting together and unpicking the pollination relationships within this family. Let’s hope that old socks is as difficult as this extraordinary work gets.